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CLEARWATER <br /> G R 0 U P, I N C <br /> ' 4.0 CONCLUSIONS AND RECOMMENDATIONS <br /> 4.1 Conclusions <br /> I , <br /> Vertical Extent of Hydrocarbons in Soil <br /> At the request of the San Joaquin County PHS, boring CPTB-7 was advanced to <br /> evaluate the vertical extent of hydrocarbons un soil between 40 and SO feet bgs. Soil <br /> samples collected at 42 to 45 feet (considered to be within the upper water-bearing <br /> ' unit at the site) contained TPHg concentrations of 13 ppm or less Two samples <br /> were analyzed from the silty clay underlying the upper aquifer, one sample <br /> contained no detectable hydrocarbons and the other contained only benzene, <br /> ethylbenzene, and toluene at concentrations slightly above the detection limits <br /> Analytical results indicate that samples below a depth of 55 feet bgs contain very low <br /> concentrations of TPHg and/or BTEX compounds Two deeper sands (A and B) were / <br /> ✓ . <br /> encountered in the boring, the samples from sand A contained no detectable --` <br /> concentrations of TPHg and the sample from sand B contained only 0 4 ppm TPHg <br /> On the basis of this data, following conclusions are made regarding the vertical <br /> extent of hydrocarbons at the site: <br /> The upper aquifer at,the site is separated from,the deeper sands by a silty clay' <br /> deposit approximately 10 feet thick ✓ ' <br /> r <br /> I <br /> •, Two samples were collected from the silty 'clay unit, hydrocarbon concentrations <br /> were either nondetectable or slightly above the detection limits I <br /> • A dark green clay layer approximately 9 feet thick separates deeper sands A and B <br /> • Hydrocarbon concentrations are higher in sand B than in sand A , <br /> � ' l <br /> ' The upper aquifer at the site appears to be stratigraphically and chemically <br /> isolated from the deeper sands encountered in CPTB-7, indicating that <br /> I hydrocarbons present in soil below approximately 50 feet on unated from 'an <br /> 1 <br /> offsite source------------ <br /> i IlI <br /> I <br /> ! <br /> E 'I Downgradient'Extent,of'DissolvedlHydrocarbons <br /> I <br /> l I I , <br /> I � I � I <br /> I <br /> � , Ill I �, f I I I I I I ' <br /> Monitormg well MW-6,was,installed to lke{valuatef the downgradient,extents of <br /> D101 PAR/3Q/PILOT , 14 <br /> � k: it 'I � i {li li II�iII ik! e��lE ilk i lis i I Iilr �I I i �I I it lll��k'i it I lI Iq I� 'h 1 ( 'i il�ll IIII II I <br /> i f�l� 14'l91 'I I i IV I !I i I I l I I I Ec I I I {i IEi E E' <br /> i ' ilI I I 6I, III I Ill Ill to lif „I,IIIk�,ll VI I it l' �',��I I l I Illi Il LIBEL,I ll fill l'l I `�� "Il l'lIll <br />